This anything like Sleeping Dogs?
Not really, as I remember that was more action and fast paced? It's a Yakuza game from a different perspective. You're not in the Yakuza, but know them and have ties to them. Partner is ex-Yakuza. So instead of being in it, you're investigating things tied to them (at least the main story so far).
I finished chapter 1 (around 5 hours), think there are 7-8 chapters? Chapter 1 is basically a tutorial. I didn't see any side missions other than the friends part, where you become "friends" by using their establishments and such. They can unlock side missions later (extra investigations I assume, not tied to the main story ones). Many of the activities are locked in chapter 1 like Drone racing which I assume is a more active racing game than the little race cars from Zero.
In chapter 1, investigation aspects are quite basic. Impossible to miss the right questions since you get to ask all of them, just need to do the correct ones first to get skill point bonuses. No idea if this changes later, into a more LA Noire thing where you can make mistakes. I did answer one wrong which led to a fight. Not sure if that also goes into later chapters in court, which can effect outcome of cases and maybe the end game? Chapter one is linear though and can't be messed up. You'll always know where to go, what to ask, where to look, which is why I call it a tutorial.
Tl;dr: So far the game has built a great base mechanic and ideas that could separate it enough from just being a Yakuza clone, but then it needs to expand on the investigations and court related things. I don't know if it does that yet.